Switch to Jekyll

Switches to Jekyll, where HTML is generated upon deploy. Coming from a system powered by the [DocumentUp](http://documentup.com/) API plus a `compile.rb` script, where HTML was frozen into the repo.

Changes:

* New pygments theme, taken from [MozMorrow/tomorrow-pygments](https://github.com/MozMorris/tomorrow-pygments). (`.err` class disabled, to allow for ellipses.)
* Switched fenced code block syntax to Jekyll (Liquid) syntax, for Jekyll-level pygments highlighting.
* TOC is now generated upon demand, but is generated in each page -- and then copied via JS upon page load. (Awful hack.)
* Each page now has a tiny bit of YAML front-matter at the top, specifying the default layout.

I wrote a [small adapt.rb script](https://gist.github.com/konklone/7935945) that can be run on all `.md` files in a directory to transform them from old to new style.

My hope is that someday, I can ditch the Jekyll highlight blocks and put the fenced code blocks back, either if:

* Kramdown adds [built-in highlighter options](https://github.com/gettalong/kramdown/pull/68#issuecomment-30207002) besides Coderay
* Redcarpet [adds support for automatic TOC generation](https://github.com/vmg/redcarpet/issues/330)
* Jekyll's Redcarpet processor [adds its own support for a TOC generation tag](https://github.com/jekyll/jekyll/issues/1774#issuecomment-30446439).

I'd also like to ditch the JS hack for moving the TOC on-load from the content into the nav, by either:

1. A custom, our-layout-specific post-processing Jekyll plugin that does this swapping at generate-time, using Nokogiri.
1. Some sort of Jekyll plugin that allows whole HTML blocks to flow up to the layout (similar to Rails/Sinatra's `content_for`)
1. Our base DocumentUp-adapted layout is reworked to allow the nav to be generated at the top of the file, but styled to the side like it is now.
1. We break the nav into a beginning, an end, surrounding where the TOC would go, then use `_includes` for the beginning and end, and move the whole nav into the body of individual pages.

1 is my favorite, but it requires plugin support in GH Pages.